Đáp án:

3. New devices to help people live a longer life had been invented by scientists.

4. Plastic bags are major sources of waste so we shouldn't throw plastic bags everywhere.

5. Aids for the homeless will be provided by the students tomorrow.

6. Although the girl worked hard, her stepmother wasn't happy.

7. Because factories produce waste and pour them into rivers and lakes, many rivers and lakes are poisoned.

8. After she had done all her homework, she watched TV.

9. Lan said that she had bought that book the week before.

10. Dr.Nelson said that there would be new advanced robots in the future.

  Những câu bạn đã làm mình sẽ không làm lại nữa nhé.

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   Có thể mình làm sai, mong bạn thông cảm =((

      -Minhh-

task 12

3. new devices have been invented to help people live a longer life 

4. plastic bags are major... waste so we shouldn't ....

5. aids will be provided for the homeless tomorrow

6. although the girl works hard, her stepmother.....

7. many rivers and lakes are poisoned because factories produce waste.....

8. after having finished all the homework, my sister watched TV 

9. lan said to me she had bought that book the previous week 

10. dr. nelson told us there would be a new advanced robots in the future